1. Technical Field
Example embodiments of the present invention generally relate to a sheet processing apparatus and an image forming apparatus including a stapling and folding mechanism, e.g., for stapling and folding sheets.
2. Description of Background Art
A background image forming apparatus forms an image on a recording medium (e.g., sheets). The sheets bearing the image may be sent to a sheet processing apparatus for performing processing on the sheets, for example, stapling and folding.
One example of a background sheet processing apparatus includes a staple tray and a fold tray. The staple tray includes an edge stapler and a center stapler. The edge stapler is provided in a lower portion of the staple tray and staples sheets at a position on an edge portion of the sheets. The center stapler is provided in a center portion of the staple tray and staples sheets at a position along the center line of the sheets in a sheet conveyance direction. Sheets sent from the image forming apparatus may be stapled either by the edge stapler or the center stapler. When the center stapler staples the sheets, the fold tray folds the sheets stapled by the center stapler along the center line of the sheets in the sheet conveyance direction to bind the sheets into a magazine.
A stapler moving motor, which is rotatable back and forth, may drive the edge stapler via a timing belt. The edge stapler may move in a direction perpendicular to the sheet conveyance direction to staple sheets at a staple position on an edge portion of the sheets. A stapler sensor may be provided in one end of a moving area of the edge stapler and detects the home position of the edge stapler. The staple position in the direction perpendicular to the sheet conveyance direction may be identified based on a distance for which the edge stapler moves from the home position.
The staple tray may further include an edge fence, a tapper, jogger fences, and a discharging belt. When sheets are delivered into the staple tray, the foremost edges of the sheets in the sheet conveyance direction may touch the edge fence and stop. The tapper may tap the tail edges of the sheets in the sheet conveyance direction. Thus, the sheets may be aligned in the sheet conveyance direction. The jogger fences move to contact the side edges of the sheets to align the sheets in the direction perpendicular to the sheet conveyance direction. The center stapler may include two staplers. The two staplers may be provided symmetrically with respect to the center line of the sheets in the direction perpendicular to the sheet conveyance direction in a manner that a distance from the edge fence to a staple position is greater than half a length of the maximum size sheet that the sheet processing apparatus can handle in the sheet conveyance direction. The discharging belt may include a discharging hook. When the sheets are aligned, the discharging belt may be driven and the rotating discharging belt may move the discharging hook attached thereto upward. The discharging hook may contact the foremost edges of the sheets contacting the edge fence and lift the sheets up to a position at which the center line of the sheets in the sheet conveyance direction is placed at the staple position of the center stapler. The center stapler may staple the sheets at the staple position. The stapled sheets may be sent to the fold tray where the stapled sheets are folded along the center line of the sheets in the sheet conveyance direction.
As described above, in a background sheet processing apparatus, the staple tray may include both the edge stapler and the center stapler. Namely, sheets may be stapled at a position on an edge portion or along the center line of the sheets in the sheet conveyance direction in the common staple tray. The maximum number of sheets which can be stapled by the center stapler may be limited to about 20 sheets because the fold tray can fold up to about 20 sheets. When sheets are stapled at a position along the center line of the sheets in the sheet conveyance direction, the sheets may be curled or buckled more easily than when the sheets are stapled at a position on an edge portion of the sheets. Therefore, in the center stapler, a clincher and a driver may be spaced by about 15 mm away from each other. As a result, the maximum number of sheets which can be stapled by the edge stapler may be limited to about 50 sheets because more than 50 sheets cannot be properly conveyed in the space between the clincher and the driver. For example, the sheets may block the space and thereby may be jammed.
When the clincher and the driver are spaced farther away from each other so that 100 sheets, for example, can be conveyed in the space between the clincher and the driver to increase the maximum number of sheets which can be stapled by the edge stapler, the sheets may be curled or buckled and thereby the center stapler may not staple the sheets at a position along the center line of the sheets in the sheet conveyance direction with a desired accuracy.